Seminar Details

Off-Line Production of Singly-Charged, Transition-Metal Beams and Subsequent Collinear Laser Spectroscopy of Neutral, Stable 55Mn and 56Fe

Andrew Klose, MSU NSCL/Chemistry
Thursday, February 28, 11:00 AM - Research Discussion
NSCL Lecture Hall

Collinear laser spectroscopy was performed on stable 55Mn and 56Fe atoms at the BEam COoler and LAser Spectroscopy (BECOLA) facility at NSCL [1]. The experiments serve as the groundwork for the planned study on the nuclear electromagnetic moments and charge radii of beta unstable isotopes via laser probing methods, where sparse data exists for light transition metals (Z = 21 to 29) [2]. The in-flight production and subsequent beam thermalization and extraction at NSCL [3] provides access to low-energy beams (< 60 keV/q) of these elements. In contrast, the same elements are extremely difficult to extract from thick ISOL-like targets, due to their low vapor pressures. The main science motivation for measuring the ground-state properties of nuclei with Z = 20 to 30 is to understand, in a microscopic basis, the onset of deformation around and across N = 28 and 40 for the neutron-rich transition metals [4]. A systematic study of the electromagnetic moments and charge radii of these isotopes may help elucidate the rich nuclear structure in this region. Such studies via collinear laser spectroscopy require the offline development of stable beams as a reference for online measurements. For this purpose, Mn+ and Fe+ beams were separately produced using two ion sources: a commercial plasma ion source with a metallic charge, and a home-built electron ionization ion source using a highly volatile metallocene charge. The produced ions were accelerated to 15 keV and co-propagated with single-mode, continuous-wave laser light. The ion beams were then neutralized via charge-exchange reactions with a Na vapor [5]. Multiple atomic levels of the outgoing atomic beam were populated in the charge-exchange reactions. One optical transition was investigated for neutral 56Fe (Ip = 0+), and two transitions were separately investigated for neutral 55Mn (Ip = 5/2-). Hyperfine structures were determined by measuring laser-induced fluorescence from the atoms as a function of effective laser frequency. The hyperfine spectra for Mn I were analyzed by simultaneously fitting all observed peaks for each transition. The A and B hyperfine coupling constants were deduced from the fits, and are consistent with known values.

References:

1. K. Minamisono, et al. Nuclear Instru. Methods A. doi:10.1016/j.nima.2013.01.038.
2. K. Blaum et al., Phys. Scripta T152 (2013) 014017.
3. L. Weissman et al., Nucl. Instrum. Methods A. 540 (2005) 245.
4. S. M. Lenzi et al., Phys. Rev. C 82 (2010) 054301.
5. A. Klose et al., Nucl. Instrum. Methods A 678 (2012) 114.